It has been said that hyperlipidemia, diabetes, hypertension or the like is one of the risk factors for arteriosclerosis. Hyperlipidemia is a condition where the concentration of lipid such as cholesterol is abnormally elevated in the blood. Types of hyperlipidemia, depending on the cause, include primary hyperlipidemia caused by genetic abnormality in enzyme, protein, lipoprotein and the like which participate in the metabolism of low-density lipoprotein (LDL), secondary hyperlipidemia due to various disease or drug administration, and acquired hyperlipidemia basically resulting from overnutrition.
Meanwhile, lipid taken in from food is absorbed in the small intestine by the action of bile acid, and secreted as chylomicron in the blood via lymphatic vessels. The triglyceride moiety of the secreted chylomicrons is hydrolyzed to free fatty acids by the action of lipoprotein lipase (LPL) existing in capillary vessels to become chylomicron remnants having a high content of cholesteryl ester (CE), which is then absorbed in the liver by the mediation of chylomicron remnant receptor in the liver. Further, in the liver, the absorbed chylomicron remnant and free fatty acid are converted to CE and TG, respectively, which are then associated with apolipoprotein B synthesized on rough surfaced endoplasmic reticulum to form very low density lipoprotein (VLDL). The VLDL is transferred to the Golgi apparatus, modified and secreted outside cells, and it becomes intermediate density lipoprotein (IDL) by the action of LPL. The IDL is converted to LDL by the action of hepatic triglyceride lipase (HTGL), and lipids are distributed to peripheral tissues.
It has long been indicated that, during the above-mentioned formation of chylomicron in the small intestine or VLDL in the liver, a protein having TG- or CE-transfer activity is existing in microsomal fractions of the small intestine or liver. Meanwhile, the protein, i.e. MTP (microsomal triglyceride transfer protein) was purified and separated from microsomal fractions of bovine liver by Wetterau et al. in 1985 (Wetterau J. R. et al: Chem. Phys. Lipids 38, 205-222(1985)). MTP, however, began attracting a lot of attention in the field of clinical medicine only after it was reported in 1993 that the cause of abetalipoproteinemia lay in the deficit of MTP. In other word, the disease is characterized in that, while the genes related to apolipoprotein B are normal, apolipoprotein B is hardly detected in the serum, the level of serum cholesterol is 50 mg/dL or lower, the level of serum triglyceride is extremely low and, moreover, lipoproteins including apolipoprotein B such as chylomicron, VLDL, LDL, etc. do not at all exist in the blood. By this finding, it has been shown that MTP is an integral protein involved in the association between apolipoprotein B and TG or CE, i.e. the formation of VLDL or chylomicron, and plays an essential role in secretion thereof.
Since lipid is by nature insoluble in water, lipid in the blood is combined with a hydrophilic protein known as apolipoprotein and exists as so-called lipoprotein. All the VLDL, IDL, LDL or chylomicron, etc. related to hyperlipidemia are a lipoprotein.
MTP exists in the microsome fractions of hepatocytes and intestinal epithelial cells, and catalyses the transfer of TG or CE in cells. In the liver and small intestine, along with the synthesis of apolipoprotein (apolipoprotein B100 in the liver and apolipoprotein B48 in the small intestine), TG and CE are combined with respective apolipoprotein B by the transfer activity of MTP, and thus VLDL or chylomicron is formed. As a result, those lipoproteins are secreted outside the cells as VLDL in the liver or as chylomicron in the small intestine. It should be said that MTP is indispensable for the construction of those lipoproteins. Namely, if the activity of MTP is blocked, the transfer of lipid such as TG and CE, etc. to apolipoprotein is inhibited, whereby formation of a lipoprotein can be inhibited.
On the other hand, it has been elucidated that LDL in general is closely related to the progression of arteriosclerosis. That is, LDL permeating endothelium of blood vessels is deposited in intercellular matrix of vessel wall, where oxidative denaturation takes place and lipid peroxides or denaturated proteins induce a series of inflammation reactions. Consequently, macrophage invasion, leading to lipid deposit or foaming cells, migration or proliferation of smooth muscle cells and increase in intercellular matrix, etc. take place, which leads to the development of arteriosclerosis plaque. On the basis of the above, it is supposed to be possible to prevent or treat arteriosclerosis, coronary artery diseases or hypertension by reducing the level of LDL.
As already mentioned, it is possible to inhibit the formation of lipoprotein such as chylomicron, VLDL, LDL, etc. by inhibiting the action of MTP. Accordingly, it has been expected that it should become possible to control lipoprotein such as TG, cholesterol and LDL, etc. in blood and to control lipid in cells by adjusting the activity of MTP, and therefore, a novel agent for the treatment or prophylaxis of hyperlipidemia, arteriosclerosis, coronary artery diseases, diabetes, obesity, or hypertension, and further, an agent for the treatment or prophylaxis of pancreatitis, hypercholesterolemia, hyperglyceridemia, etc. has been expected to be provided.
However, with the development of MTP inhibitors, some cases of fatty liver were reported and concern over hepatotoxicity has been raised.
For these reasons, a novel MTP inhibitor causing no side effect such as a fatty liver, etc. has been strongly desired.
In the conventional manners, combined therapies of various combinations of different antihyperlipidemic drugs have been tried. However, when, for example, astatin-type drug and a resin-type drug are given together, undesirable side effects such as increased GTO and GPT, constipation, blocking of absorption of vitamin A, D, E and K and the like are observed. On the other hand, when a statin-type drug and a fibrate drug are given together, side effects such as rhabdomyolysis or increased CPK (creative phosphokinase) are observed. Thus, with regard to a combined therapy for hyperlipidemia, a medicament for a combined administration which can be administered in combination with a conventional antihyperlipidemic drug without causing any above-mentioned side effect has been desired.
Meanwhile, examples of the known compound having MTP inhibitory activity with a similar structure of the compounds of the present invention are described below.
The following compound is disclosed in WO97/26240.

The following compound is disclosed in WO97/43257.

The following compound is disclosed in WO98/23593.

The following compound is disclosed in WO99/63929.

The following compound is disclosed in WO2000/5201.

The following compound is disclosed in J. Med. Chem. (2001), 44(6) p. 851-856.

The following compound is disclosed in EP 1099701.

The following compound is disclosed in WO2001/77077.

The following compound is disclosed in J. Med. Chem. (2001), 44(6) p. 4677-4687.

The following compound is disclosed in WO2002/4403.

In the above literatures, however, there is no disclosure of a compound comprising ester as the essential structure as that disclosed in the present invention, much less the disclosure of the data indicating that when a compound has the structure disclosed in the present invention, the compound selectively inhibits MTP in the small intestine while rarely affects MTP in the liver.